Process for the production of high molecular weight copolymers of diallyl ammonium monomers and acrylamide monomers in solution

ABSTRACT

Water-soluble, high molecular weight, linear copolymers of a diallyl ammonium monomer and an acrylamide monomer of various cationicities are prepared by copolymerization of a major portion of the acrylamide monomer via stage-addition in a solvent solution and adding a chain transfer agent at the conclusion of said copolymerization to prevent branching and cross-linking from occurring.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional of application Ser. No. 07/667 707, filed Mar. 11,1991, now U.S. Pat. No. 5,110,883.

This invention relates to high molecular weight, water soluble, linearcopolymers of diallyl ammonium monomers and acrylamide monomers havingvarying cationicities, and to methods of preparing the same. Copolymersof this type are useful as cationic flocculants in the treatment ofindustrial water, as sludge conditioners for the treatment of municipalwater systems, and as drainage and retention aids in the manufacture ofpaper.

Diallyl ammonium monomers are quaternary monomers, which whenpolymerized, yield water soluble polymers that are cationic in nature.The polymerization of acrylamide monomers, on the other hand, produceswater soluble polymers that are essentially nonionic in nature. Thus,the copolymerization of diallyl ammonium monomers and acrylamidemonomers results in the formation of water soluble copolymers havingvarious degrees of cationicity, depending upon the amount of diallylammonium monomer that is incorporated into the final copolymer.

The copolymerization of diallyl ammonium monomers and acrylamidemonomers in solution is well known. U.S. Pat. No. 2,923,701, forexample, describes the simultaneous copolymerization of acrylamide anddiallyl dimethyl ammonium chloride in solution by the addition of aredox catalyst, such as ammonium persulfate and potassium metabisulfite,to an aqueous mixture of the monomers.

U.S. Pat. No. 3,147,218 discloses the use of diallyl ammonium monomersand acrylamide monomers based copolymers for the separation of mineralfines. European Patent Application 103 698 describes the preparation ofacrylamide and diallyl ammonium monomer based copolymers via thepolymerization of a solution of the corresponding monomers in thepresence of a free radical initiator. The solvent is removed bypolymerizing and drying the resulting polymer solution at a temperatureabove the boiling point of the solvent.

Copolymers of diallyl ammonium monomers and acrylamide monomers can alsobe obtained utilizing emulsion polymerization techniques in accordancewith the teachings of U.S. Pat. No. 3,920,599. Stable water-in-oilcopolymer emulsions are prepared, which can then be inverted by means ofsuitable hydrophilic, water-soluble surfactants. U.S. Pat. No. 4,070,930discloses the preparation of stable emulsion copolymers of diallylammonium monomers and acrylamide, which can be inverted by the additionof water. European Patent Application 0 188 721 provides an improvedprocess for the incorporation of diallyl ammonium monomer into anacrylamide monomer based polymer by means of either emulsion or solutionpolymerization techniques. This improvement comprises the step ofpolymerizing diallyl ammonium monomers and acrylamide monomers in thepresence of a copolymerizable monomer, such as a quaternary substitutedacrylamide or methacrylamide. The monomer utilized must have a greaterreactivity than a diallyl ammonium monomer with an acrylamide monomer.

The present invention relates to a process for the preparation of highmolecular weight, water-soluble, linear copolymers of diallyl ammoniummonomers and acrylamide monomers having a uniform diallyl ammoniummonomer to acrylamide monomer ratio. More particularly this processcomprises the steps of:

a) initiating the copolymerization of a stirred mixture of diallylammonium monomer with a portion of the total amount of the acrylamidemonomer required in a solvent solution at a temperature at whichcopolymerization proceeds;

b) adding to said stirred monomer solution the remaining acrylamidemonomer via continuous stage addition, preferably over a period of fromabout 0.5 to about 8 hours at a temperature at which copolymerizationproceeds;

c) homogeneously mixing a chain transfer agent in said gel solution toform a gel mixture;

d) heating said gel mixture to minimize residual monomer content,preferably to a temperature of from about 60° to about 90° C. for aperiod of from about 0.1 to about 4 hours;

e) drying said gel mixture, and recovering the desired copolymertherefrom.

This invention also relates to high molecular weight water solublelinear copolymers of diallyl ammonium monomers and acrylamide monomersprepared in accordance with the process of this invention. Suchcopolymers are particularly useful as flocculants for sludgeconditioning in the treatment of municipal and industrial water andwaste water systems over a wide range of pH. The copolymers describedherein are also useful as drainage and retention aids in the manufactureof paper.

As previously indicated, the preparation of diallyl ammonium monomer andacrylamide monomer based copolymers is well known. In general, however,the existing prior art copolymers are non-uniform in their compositionand tend to be highly branched and cross-linked. In addition, the priorart copolymers are of relatively low molecular weight, and/or haveintrinsic viscosities generally less than 6 dl/g.

The present invention overcomes these deficiencies of the prior art andenables the preparation of high molecular weight copolymers from diallylammonium monomers and acrylamide monomers having intrinsic viscositiesranging from 10 to 25 dl/g. More particularly, diallyl ammonium monomerand acrylamide monomer based copolymers are prepared in accordance withthis invention that have intrinsic viscosities ranging from 15 to 20dl/g. It is generally recognized by those skilled in the art thatintrinsic viscosity is an indication of polymer molecular weight. Thus,the higher the intrinsic viscosity, the greater is the molecular weightof the particular polymer or copolymer prepared.

When prepared in accordance with the teachings of this invention,copolymers of varying cationicities can be prepared. Moreover, suchcopolymers are uniform in composition. That is to say, copolymers areprepared which contain little, if any, residual monomer, and which havea uniform diallyl ammonium monomer to acrylamide monomer ratiothroughout the entire length of the copolymer chain.

One difficulty in the preparation of diallyl ammonium monomer andacrylamide monomer based copolymers, have a uniform distributionthroughout the length of the copolymer chain, is due to the differencein reactivity of the acrylamide monomer as compared to the diallylammonium monomer. This difference in reactivity results in a non-uniformdistribution of the diallyl ammonium monomer throughout the copolymerchain. Thus, at the onset of the copolymerization reaction, a relativelylarger number of acrylamide monomer units are initially incorporatedinto the polymer chain due to the greater reactivity of the acrylamidemonomer. Accordingly, at the conclusion of the copolymerizationreaction, relatively more of the diallyl ammonium monomer units remainunused and remain either as free monomer, or form low molecular weighthomopolymers. These excess diallyl ammonium monomers or low molecularweight diallyl ammonium homopolymers remain either as a residual mixtureor they become incorporated within the copolymer chain, which results ina non-uniform distribution of copolymer units throughout the copolymerchain. This is particularly true in the case of copolymers wherein thefinal diallyl ammonium content is greater than 20% on a molar basis ofthe total copolymer content.

A further difficulty in the preparation of high molecular weight linearcopolymers of diallyl ammonium monomers and acrylamide monomers is dueto the manner in which the diallyl ammonium monomers polymerize.Normally, the diallyl ammonium monomers polymerize by incorporating bothof the allyl bonds within the same molecule to form a linear polymerchain. A small proportion of the diallyl ammonium monomer, however, canpolymerize via the incorporation of only one of its allyl bonds, therebyleaving a pendant double bond remaining in the molecule. These pendantdouble bonds can subsequently initiate branching, particularly at highertemperatures, to produce cross-linked polymers that have a reducedsolubility in water, see Jaeger et al., Journal of MacromolecularScience, Part A Chemistry, 593-614, (1984).

This greater reactivity of the acrylamide monomer in combination withthe tendency of the diallyl ammonium monomer to polymerize via branchingor cross-linking, results in the formation of non-linear diallylammonium monomer and acrylamide monomer based copolymers havingrelatively low intrinsic viscosities, and which are not particularlywell suited as flocculants in water and waste water system for sludgeconditioning, or as drainage and retention aids in the manufacture ofpaper. These problems have been overcome by means of the presentinvention, which enables the preparation of high molecular weight,linear copolymers of diallyl ammonium and acrylamide monomers of uniformcomposition that have little, if any, branching and cross-linking in thepolymer chain.

The diallyl quaternary ammonium compounds preferably correspond to theformula ##STR1## wherein R¹ is independently in each occurrence ishydrogen or C₁₋₄ alkyl; R² is independently in each occurrence C₁₋₁₈alkyl, C₁₋₁₈ alkoxyalkyl or C₁₋₁₈ hydroxyalkyl moieties; and Y is ananion, which does not sustantially interfere with the polymerizationreaction.

Illustrative examples of radicals represented by R² in Formula 1 aremethyl to octadecyl, inclusive; hydroxymethyl and the varioushydroxyethyl to hydroxyoctadecyl, inclusive; and methoxymethyl and thevarious high alkoxy (e.g., methoxy to octadecocy, inclusive) alkyls,e.g., ethyl to octadecyl inclusive. Illustrative examples of anionsrepresented by Y in Formula I are the halide ions (that is, Y canrepresent halogen, more particularly chlorine, bromine, fluorine oriodine), sulfate, sulfonate, phosphate, hydroxide, borate, carbonate,thiosulfate, isocyanate, oxalate, silicate, sulfide, cyanate, acetateand the other common inorganic and organic ions. Specific examples ofcompounds embraced by Formula I are the diallyl, dimethallyl, diallyldimethyl and diethallyl dimethyl, di (beta-hydroxyethyl) anddi(beta-ethoxyethyl) ammonium chlorides, bromides, phosphates andsulfates. Other examples will be apparent to those skilled in the artfrom Formula I and from the numerous examples of anions represented by Yand of radicals represented by R² that have been given hereinbefore withreference to the said formula.

R¹ is preferably hydrogen, methyl or ethyl; methyl or even morepreferably hydrogen or methyl; and most preferably hydrogen. Y ispreferably a halide ion, and most preferably a chloride ion. In a mostpreferred embodiment the diallyl quaternary ammonium compound is diallyldimethyl ammonium compound; the most preferred diallyl dimethyl ammoniumcompound is diallyl dimethyl ammonium chloride (DADMAC).

Acrylamide compounds as used herein refers to acrylamide,methacrylamide, and derivatives thereof wherein the alpha carbon may besubstituted with a C₁₋₅ lower alkyl moiety and the amide nitrogen may besubstituted with a C₁₋₁₈ alkyl moiety, C₁₋₁₈ alkyloxy moiety or C₁₋₁₈hydroxy alkyl moieties. Such acrylamide compounds preferably correspondto the formula ##STR2## wherein

R³ is independently in each occurrence hydrogen, or a C₁₋₅ lower alkylmoiety;

R⁴ is independently in each occurrence hydrogen C₁₋₁₈ alkyl, C₁₋₁₈alkoxy, or C₁₋₁₈ hydroxy substituted alkyl. R³ is preferably hydrogen ormethyl, and most preferably hydrogen. R⁴ is preferably hydrogen or C₁₋₁₈alkyl; more preferably hydrogen or C₁₋₈ lower alkyl, and most preferablyhydrogen or methyl.

In general, the process of this invention essentially utilizes acontrolled addition or stage-addition of the acrylamide monomer duringthe copolymerization reaction. Surprisingly, it has been discovered thatthis continuous stage-addition of the acrylamide monomer produces highmolecular weight copolymers of diallyl ammonium and acrylamide monomerswhich heretofore have not, as yet, been available. Additionally,copolymers having high diallyl ammonium monomer conversions can beprepared that contain a uniform distribution of diallyl ammonium monomerand acrylamide monomer units throughout the entire length of thecopolymer chain with little, if any, residual diallyl ammonium monomeror acrylamide monomer remaining in the finished product. In addition,the process of this invention also utilizes the addition of a chaintransfer agent to prevent branching and cross-linking of the polymerchain from occurring, particularly at elevated temperatures.

The impurities in the starting monomers can affect the overallproperties of the final polymer. The starting monomers should besufficiently pure to prepare linear copolymers with relatively constantdiallyl ammonium monomer to acrylamide monomer ratios along the chainand which has an intrinsic viscosity of from about 10 to 25 d/l. In apreferred embodiment, wherein the diallyl ammonium monomer is DADMAC andthe acrylamide monomer is acrylamide, DADMAC has no more than about 50ppm of allyldimethylamine; about 100 ppm of dimethylamine, and about 10ppm of allyl alcohol. Preferably, the acrylamide has no more than 1200ppm of nitrilotrispropionamide, and 10 ppm of methoxyhydroquinone.

To initiate copolymerization, a portion of the acrylamide monomer isadded to the total amount of diallyl ammonium monomer that is requires.Preferably, about 12 to about 20% of the total amount of the acrylamidemonomer is initially added to the reaction mixture. More preferably,from about 15 to about 17% of the total amount of the acrylamide monomerrequired is generally added to initiate copolymerization. Thecopolymerization reaction of the diallyl ammonium monomers and theacrylamide monomers is an exothermic reaction. Thus, oncecopolymerization begins, the temperature of the reaction mixture rapidlyincreases. At this point the remaining amount of acrylamide monomer isintroduced to the reaction mixture via a process of stage-addition.After all of the acrylamide monomer has been stage-added to the reactionmixture, a chain transfer agent is added in order to prevent anybranching or cross-linking of the polymer chain from occurring.

The copolymerization reaction is conducted in solution in the presenceof a suitable solvent. A suitable solvent is a solvent which dissolvesthe reactants and which does not deleteriously affect the finalproperties of the copolymer produced. Preferable solvents include water,primary alcohols having from 1 to 4 carbon atoms, and aqueous mixturesthereof. The use of lower alcohols has the advantage that it can providea granular product that is easier to handle and that can be more readilydried. However, inasmuch as both the starting materials and finalproducts are soluble in water, water is generally the solvent of choice.

Sufficient solvent should be employed to facilitate polymerization andto homogeneously dissolve all of the components of the reaction mixture.Aqueous monomer solutions containing from about 40 to about 70% ofmonomer are preferably employed as starting solutions. Preferably,aqueous monomer solutions containing from about 50 to about 60% monomerare generally employed. If necessary, additional water can be added tothe reaction mixture during the course of the reaction in order toprovide optimum conditions for polymerization and adequate mixing.

One important aspect of this invention is that copolymers of varyingcationicities can be precisely prepared in accordance with the processof this invention. The greater the number of diallyl ammonium monomerunits introduced into the polymer chain, the greater will be thecationicity of the resulting copolymer. Thus, copolymers useful ascationic flocculants in water clarification systems or as sewagedewatering agents, require copolymers having a higher degree ofcationicity than cationic flocculants useful as drainage and/orretention aids in the manufacture of paper. The copolymer contemplatedby the present invention range from about 5 to about 95 mole %cationicity. That is to say, in a copolymer consisting of 100 monomerunits, the copolymers described herein comprise from about 5 to about 95diallyl ammonium monomer units, and conversely from about 95 to about 5acrylamide monomer units. Preferably, copolymers comprising from about 5to about 75 mole % cationicity can be prepared. Still more preferably,polymers having from about 10 to about 50 mole % cationicity can beprepared in accordance with the teachings of this invention.

The period of time during which stage addition occurs is dependent uponthe amount of diallyl ammonium monomer units that are to be introducedinto the polymer chain. Thus to prepare a copolymer having a 10 mole %cationicity stage addition of about one hour is preferably used, whereasto prepare a copolymer having 30 mole % cationicity stage addition ofabout 3 hours is preferably used. To prepare copolymers having up to 90mole % cationicity stage addition of about 8 hours is preferably used.These periods of time will, of course, vary slightly depending upon thetype and design of reactor employed, the degree of mixing and thetemperature at which the copolymerization is conducted. For large scalepreparations, the particular parameters to be employed can be optimizedvia standard procedures known to those skilled in the art.

Preferably, the stage-added acrylamide monomer solution is continuouslyintroduced in such a manner that a slightly decreasing feed rate isachieved throughout the total period of stage addition. Thus, forexample, in a more preferred embodiment during the first quarter of theperiod for stage addition, from about 30 to about 35% of the remainingacrylamide monomer solution is stage-added; during the second quarter ofthe stage-addition period, about 25 to about 30% of the acrylamidemonomer solution is stage-added; during the third quarter about 20 toabout 25% of the monomer solution is stage-added; and the final fromabout 15 to about 20% of the acrylamide monomer solution is introducedduring the final quarter of the stage addition period. For theproduction of large quantities of copolymers, a metering pump can beadvantageously employed.

The copolymerization reaction is generally initiated using free radicalpolymerization techniques known to those skilled in the art. Compoundswhich form mainly water soluble radicals are suitable as polymerizationinitiators. For example, azostarters such as2,2-azobis-(N,N'-dimethylene-isobutyramidine) dihydrochloride,2,2'-azobis-(2-amidinopropane) dihydrochloride,2,2'-azobis-(N,N'dimethyleneisobutyramidine),4,4'-azobis-(4-cyanopentane-carboxylic acid),2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2'-azobis(2,4-dimethylvaleronitrile),(1-Phenylethyl)azodiphenylmethane, 2,2'-azobisisobutyronitrile, dimethyl2,2'-azobisisobutyrate, and 2,2'-azobis-(2-methyl-butyronitrile) can beemployed.

Additionally, peroxide polymerization initiators can be employed, as forexample, dibenzoyl peroxide, dilauryl peroxide,di-2-ethylhexylperoxydicarbonate, dicyclohexylperoxydicarbonate,bis-(4-tert. butylcyclohexyl)peroxydicarbonate, tert. butylperpivalate,tert. butyl-perbenzoate, tert. butylpermaleinate, di-tert.butyl-peroxide, tert.-butylhydroperoxide, hydrogen peroxide, ammoniumpersulfate, potassium persulfate, sodium persulfate, and redox catalystsin combination with reducing agents such as iron(II)-ammonium sulfate,ascorbic acid, sodium methyl sulfinate, disodium disulfite and sodiumhydrogen sulfite can be employed. These initiators can be used eitheralone or in combination with one another.

The rate of decomposition of the more readily decomposed peroxides canbe reduced by the addition of organic metal complex compounds, as forexample, copper acetyl acetonate. Thus the rate of peroxidedecomposition can be adapted, for example, to the particularpolymerization temperature selected. Preferred redox catalysts are thoseselected from one or several peroxides in combination with a reducingagent. Especially preferred are persulfates or peresters or mixtures ofpersulfates and peresters as a component of the redox polymerizationinitiators. The polymerization initiators are preferably used in amountsranging from about 0.001 to about 5% by weight, and more preferably fromabout 0.02 to about 2% by weight, in relation to the amount of monomersutilized.

It is preferable to keep the reaction mixture well mixed and in intimatecontact with the stage-added acrylamide monomer throughout the entirestage-addition process, in order to obtain a homogeneous distribution ofdiallyl ammonium monomer throughout the copolymer chain. Insufficientmixing results in a non-homogeneous polymerization, whereas too rapid ortoo intensive mixing results in polymer degradation. Adequate mixing ofthe copolymerization mixture is of particular importance in the latterstages of the copolymerization due to the gel which forms.

The degree and amount of mixing required to homogeneously blend thereaction mixture varies widely depending upon the size and the shape ofthe particular apparatus employed. Reaction mixers used in thepreparation of gels or other similar materials, that provide intimatemixing and kneading via a shearing action, are particularly well suitedto this process. During the latter stages of polymerization a gelsolution forms which becomes progressively more and more viscous. Thisgel solution may require additional water as well as additional mixingtime in order to obtain a homogeneous reaction mixture.

The preferred temperature at which polymerization occurs, and is thusinitiated, ranges from about 20° to about 50° C. More preferably,polymerization is initiated and conducted at a temperature ranging fromabout 30° to about 40° C. Still more preferably a temperature of 35° C.is employed. Copolymers of diallyl ammonium monomers and acrylamidemonomers prepared at a temperature of 35° C. are completely soluble inwater, irregardless of how large their molecular weights are. On theother hand, copolymers prepared at temperatures above 40° C. tend to beinsoluble or partially insoluble. This insolubility is the result of theincreased tendency for the diallyl ammonium monomer to polymerize viabranching and cross-linking at higher temperatures. The more branchedand cross-linked the copolymers become, the less soluble they are inwater. Indeed, one of the qualitative tests for the degree of branchingand cross-linking for this type of copolymer is its solubility in water.

Inasmuch as the polymerization reaction is exothermic in nature, controlof the reaction temperature is important. In order to maintain closecontrol over the reaction temperature, the boiling point of theparticular reaction solvent mixture is utilized. Thus, where water isemployed as the reaction solvent, the reaction is conducted under areduced pressure ranging from about 35 to about 60 millibars, preferablyfrom about 50 to about 55 millibars pressure, in order to maintain aconstant temperature of 35°±1.0° C. Following the stage addition of allof the acrylamide monomer solution, the reaction mixture is stirred foran additional period of from about 30 minutes to about 1 hour at a thepolymerization temperature in order to complete polymerization.Preferably, polymerization occurs at temperatures of from about 20° toabout 50° C. More preferably, polymerization is conducted at atemperature ranging from about 30° to about 40° C., and most preferablyabout 35° C.

After the completion of the polymerization reaction, the reaction vesselis brought to atmospheric pressure utilizing nitrogen or some otherinert gas. A polymerization reaction regulator or chain transfer agentis added to the gel solution with mixing in order to prevent branchingand cross-linking from occurring. Preferable chain transfer agentsinclude, for example, lower alkyl alcohols having from 1 to 5 carbonatoms, mercaptoethanol, mercaptopropanol, thioglycolic acid,dodecylmercaptan, formic acid, halogenated hydrocarbons, such asbromoethane or carbon tetrachloride, and sodium hypophosphite. Morepreferably, a solution of sodium hypophosphite is employed. The chaintransfer agents are preferably used in amounts ranging from 0 to about3% by weight with respect to the monomers employed and must bethoroughly mixed with the gel mixture.

Following the addition of the chain transfer agent, the reaction mixtureis heated to a temperature at which residual monomer undergoespolymerization, preferably about 60° to about 90° C. and more preferablyabout 75° C. and maintained at that temperature for a period sufficientto polymerize most of the residual monomer remaining, preferably for atime of from about 0.1 to about 4.0 hours. This period of heating servesto minimize the residual monomer content of the copolymer produced. Thisis especially important with respect to any residual acrylamide monomerthat may be present, so that copolymers are prepared that areenvironmentally compatible.

The gel mixture containing the desired product is cooled, dischargedfrom the reactor and dried. Alternatively, prior to drying, the gelmixture can be extruded and granulated in order to assist the finaldrying step. The product so prepared can be dried using any well knownmeans for drying, as for example, a fluidized bed, a circulating airconveyer, vacuum drying or microwave drying. The dried product isobtained as a white, granular, pourable material, which is completelysoluble in water, and which preferably has an intrinsic viscosity, asdetermined by viscosity measurements in a 4% sodium chloride solution,ranging from about 10 to about 25 dl/g.

The following methods can be used to qualitatively and quantitativelydetermine the degree of diallyl ammonium monomer incorporation into thefinal copolymer.

(1) Solubility in Methanol

Copolymers of DADMAC and acrylamide having a DADMAC content greater than30 mole % are soluble in methanol. Copolymers in the range of 30 mole %are soluble in methanol, if, in addition, the methanol contains 10-20%water. Copolymers of low DADMAC content, as well as the homopolymers ofacrylamide are totally insoluble in methanol or mixtures of 80% methanoland 20% water. The fact that the 50 mole % copolymer of Example 4 andthe 30 mole % copolymer of Example 3 are soluble in methanol and a 15methanol-water mixture (80% /20%), respectively, demonstrates that nohomopolyacrylamides or copolymers of low DADMAC content are present inthese copolymers.

(2) Colloidal Titration Using Potassium Polyvinyl Sulfate

Using the method described by W Schempp et al., Papier, 36 (10A), 41-6(1982), the cationicity of the various copolymers produced can bedetermined. This procedure provides a method for determining thecationic charges bound to the particular polymer tested as expressed ineq/kg. Comparison with the theoretical calculated values, enables thecalculation of the degree of diallyl ammonium monomer conversion.

The copolymers produced in accordance with this invention are used asaids in the dewatering of a wide variety of aqueous suspensions. Thesecopolymers are particularly useful in the dewatering of organic sludgesuspensions that are proteinaceous in nature or the dewatering ofsuspensions that have been obtained by the biological degradation ofsuch matter. Such suspensions can be derived from raw or processedsewage, food waste, and fermentation effluents. The copolymers of thisinvention are also useful in the clarification of various types ofindustrial waste waters.

It is frequently desirable to dewater such sludges or suspensions inorder to facilitate their removal and their disposal. Dewatering can beeffected by the addition of an appropriate amount of the copolymer as aflocculating agent prior to the physical removal of water. Dewatering ofsludges or suspensions is usually effected by the addition of an aqueoussolution of the polymer having a concentration ranging from about 0.01to about 1% by weight of polymer. Preferably from about 0.05% to about0.5% of copolymer solution is employed. Typical addition rates forsewage sludge are in the range from about 0.2 to about 1.0% of polymerper total weight of sewage solids.

The copolymers of this invention are also useful in the paper industryas drainage and retention aids in the manufacture of paper, and in thedewatering of aqueous effluents containing cellulosic fibers. Such usesinclude, for example, treating aqueous waste water from a paper millprior to discharge of the effluent, or treating return process water forthe papermaking process. Such water may contain suspensions of celluloseor other finely divided particles in concentrations ranging from about50 ppm to about 1 or 2% by weight of solution. The copolymers of thisinvention are particularly useful and are generally employed assolutions of about 0.01 to about 1%. However, it is sometimes moreconvenient to prepare stock solutions of about 1 to about 2%, from whichthe copolymers can be utilized.

The invention described and claimed herein is more particularlyillustrated in conjunction with the following examples, which are notintended to limit the invention in any way.

EXAMPLE 1

To 2.89 kg of a 60% aqueous solution of DADMAC is added 2.11 kg of a 50%aqueous solution of acrylamide, 3.31 kg of water, 27 g of a 40% aqueoussolution of the pentasodium salt of diethylenetriaminepentaacetic acid,2 g of 2,2-azobis(N,N'dimethyleneisobutyramidine) dihydrochloride, 5 gof 2,2'-azobis(2-amidinopropane) dihydrochloride, and 27 g of sodiumpersulfate in a 30 liter horizontal reaction vessel equipped with amixing shaft, heating jacket, vacuum control, reflux condenser and inletports for stage addition. The reaction mixture is deoxygenated byrepeatedly evacuating the system and purging it with nitrogen. Thisprocess is repeated two additional times to insure completedeoxygenation.

The reaction mixture is heated with stirring to initiate polymerization.Once polymerization begins, the reaction is evacuated to 50-55 millibarsin order to maintain a close temperature control of the exothermicreaction. As soon as an increase in temperature is observed, theremaining 11.62 kg of a 50% aqueous solution of acrylamide, and anadditional 3.0 g of 2,2'-azobis (N,N'-dimethyleneisobutyramidine)dihydrochloride in water is added over a period of one hour, viastage-addition, with constant stirring. The feed rate is adjusted sothat approximately 29% of the acrylamide solution is added during thefirst quarter of the total time period, 26% is added during the secondquarter, 24% during the third quarter, and the remaining 21% of theacrylamide solution is added during the last quarter of the total timeperiod of one hour.

After all of the acrylamide monomer solution has been stage-added, thereaction mixture is stirred for an additional 40 minutes whilemaintaining the reaction temperature at 35° C. The reaction vessel isbrought to atmospheric pressure with nitrogen and 0.5 kg of a 10%aqueous sodium hypophosphite solution is added to the gel solution overa 30 minute period, taking care to mix the sodium hypophosphite solutioncarefully into the gel mixture. The temperature of the reaction mixtureis raised to 75° C. and maintained for a period of 2 hours toeffectively reduce any residual monomer that remains.

The gel mixture is discharged into a simple granulator and dried in afluid bed drier at 90° C. for 50 minutes to produce a dry, whitegranular copolymer comprising 10 mole % cationicity and having a uniformdistribution throughout the polymer chain. This copolymer has anintrinsic viscosity of 16 dl/g when measured in 4% sodium chloridesolution at 25° C. using a Brookfield LVT with a UL adapter. The actualcationicity as determined by potassium polyvinyl sulfate titration showsa cationicity of 1.24 eq/kg as compared to a theoretical cationicity of1.25 eq/kg (99% DADMAC conversion). The copolymer is soluble in waterand insoluble in methanol.

EXAMPLES 2-4

Following essentially the same procedure as in Example 1, but making theequivalent substitutions shown below, copolymers of varyingcationicities are obtained. All weights are expressed in kg.

    ______________________________________                                        Example         2          3       4                                          ______________________________________                                        Initial DADMAC charge                                                                         4.33       7.57    11.57                                      (60% solution)                                                                Initial Acrylamide charge                                                                     1.87       1.56    1.08                                       (50% solution)                                                                Water           3.60       3.05    1.98                                       Pentasodium salt of                                                                           0.023      0.023   0.022                                      diethylenetriamine-                                                           pentacetic acid                                                               (40% solution)                                                                2,2'azobis(2-amidine-                                                                         0.005      0.005   0.005                                      propane)dihydrochloride                                                       Sodium persulfate                                                                             0.027      0.027   0.027                                      2,2'azobis(N,N'-dimethylene-                                                                  0.002      0.002   0.002                                      isobutyramidine)                                                              dihydrochloride                                                               Stage additon-50%                                                                             10.13      7.75    5.30                                       acrylamide solution                                                           Stage additon-2,2'-azo-bis-                                                                   0.003      0.003   0.003                                      (N,N'-dimethylene-                                                            isobutyramidine)                                                              dihydrochloride                                                               Sodium hypophosphite                                                                          0.5        0.5     0.5                                        (10% solution)                                                                Reaction Temperature (°C.)                                                             35         35      35                                         Stage Addition (hrs)                                                                          2          3       4                                          pH of reaction mixture                                                                        7          7       7                                          ______________________________________                                    

The copolymers of DADMAC and acrylamide so obtained have the followingproperties:

    ______________________________________                                        Example           2         3       4                                         ______________________________________                                        Cationicity (mole %)                                                                            16        30      50                                        Cationic Titration (eq/kg)                                                    Theoretical       1.87      2.6     4.3                                       Actual            1.73      2.6     3.8                                       DADMAC Conversion (%)                                                                           92.5      85      89.3                                      *Intrinsic Viscosity (dl/g)                                                                     12.8      12.5    13.3                                      Solubility Water  sol       sol     sol                                       Solubility Methanol                                                                             insol     **insol sol                                       ______________________________________                                         *4% NaCl at 25° C.                                                     **Sol 80% methanol/20% water                                             

COMPARATIVE EXAMPLES 5-8

Following essentially the same procedures described in Examples 1-4, butwithout the stage adding of the acrylamide monomer, copolymers havingthe following properties were obtained.

    ______________________________________                                        Example          5       6       7     8                                      ______________________________________                                        Cationicity (mole %)                                                                           10      16      30    50                                     Cationic Titration (eq/kg)                                                    Theoretical      1.25    1.87    3.05  4.3                                    Actual           0.40    0.67    1.37  2.09                                   DADMAC Conversion (%)                                                                          32      36.1    45    48.7                                   ______________________________________                                    

As evidenced by the poor rates of DADMAC conversion and correspondinglack of cationicity, these non-uniform copolymers of DADMAC andacrylamide are unsuitable as flocculants for sludge conditioning in thetreatment of municipal and industrial water waste systems.

EXAMPLE 9

Following essentially the same procedure described in Examples 1-4, butomitting the use of sodium hypophosphite as a chain transfer agent,cross-linked DADMAC and acrylamide copolymers are obtained which areinsoluble in water. Such copolymers are not suitable for use asflocculating agents, due to their lack of solubility.

I claim:
 1. A water-soluble, linear copolymer of diallyl ammoniummonomer and an acrylamide monomer having a uniform diallyl ammoniummonomer to acrylamide monomer ratio and an intrinsic viscosity of fromabout 10 to about 25 dl/g as determined in a 4% sodium chloridesolution.
 2. A copolymer as claimed in claim 1 wherein the diallylammonium monomer corresponds to the formula: ##STR3## and the acrylamidemonomer corresponds to the formula: ##STR4## wherein R1 is independentlyin each occurrence hydrogen or C₁₋∝ alkyl; R² is independently in eachoccurrence hydrogen, a C₁₋₁₈ alkyl, C₁₋₁₈ alkoxyalkyl or C₁₋₁₈hydroxyalkyl moiety; R³ is independently in each occurrence hydrogen ora C₁₋₅ lower alkyl moiety; R⁴ is independently in each occurrencehydrogen, C₁₋₁₈ alkyl, C₁₋₁₈ alkoxy alkyl, or C₁₋₁₈ hydroxyalkyl; and Yis an anion.
 3. A copolymer as claimed in claim 2, wherein saidintrinsic viscosity is from 15 to 20 dl/g.
 4. A water-soluble, linearcopolymer of a diallyl ammonium monomer and an acrylamide monomer havinga uniform diallyl ammonium monomer to acrylamide monomer ratio preparedby the process comprising the steps of:a) initiating thecopolymerization of a stirred mixture of diallyl ammonium monomer with aportion of the total amount of acrylamide monomer required in a solventsolution at a temperature at which copolymerization proceeds; b) addingto said stirred monomer solution the remaining acrylamide monomer bycontinuous addition to form a homogeneous gel solution, whilemaintaining the reaction temperature; c) after completion of theaddition of acrylamide, maintaining the reaction mixture at thepolymerization temperature for a period of about 30 minutes to about 1hour to complete polymerization; d) after the polymerization iscompleted homogeneously mixing a chain transfer agent in said gelsolution to form a gel mixture; e) heating said gel mixture to atemperature at which residual monomer undergoes copolymerization; and f)drying said gel mixture.
 5. A copolymer prepared by the processaccording to claim 4 wherein the diallyl ammonium monomer corresponds tothe formula: ##STR5## and the acrylamide monomer corresponds to theformula: ##STR6## wherein R1 is independently in each occurrencehydrogen or C1-4 alkyl; R2 is independently in each occurrence hydrogen,a C1-18 alkyl, C1-18 alkoxyalkyl or C1-18 hydroxyalkyl moiety; R3 isindependently in each occurrence hydrogen or a C1-5 lower alkyl moiety;R4 is independently in each occurrence hydrogen, C1-18 alkyl, C1-18alkoxy alkyl, or C1-18 hydroxyalkyl; and Y is an anion.
 6. A copolymerprepared by the process as claimed in claim 5, wherein the solvent iswater or C1-C4 primary alcohol.
 7. A copolymer prepared by the processas claimed in claim 6, wherein the polymerization temperature of stepsa) b) and c) is about 20° to about 50° C.
 8. A copolymer prepared by theprocess as claimed in claim 7, wherein about 15 to about 17 percent ofthe total amount of the acrylamide monomer is added to step (a).
 9. Acopolymer prepared by the process as claimed in claim 8, wherein theaddition of the remaining acrylamide monomer in step (b) is over aperiod of about 0.5 to about 8 hours.
 10. A copolymer prepared by theprocess as claimed in claim 9, wherein the remaining acrylamide monomeris added in such a manner that a decreasing feed rate is achieved overstep b).
 11. A copolymer prepared by the process as claimed in claim 10,wherein from about 30 to about 35% of the remaining acrylamide monomeris added during the first quarter of step b) period, from about 25 toabout 30% is added during the second quarter, from about 20 to about 25%is added during the third quarter and from about 15 to about 20% isadded during the final quarter.
 12. A copolymer prepared by the processas claimed in claim 11, wherein the chain transfer agent is sodiumhypophosphite.
 13. A copolymer prepared by the process as claimed inclaim 11, wherein the heating of step (e) is conducted at about 60° toabout 90° C. for about 0.1 to about 4.0 hours.
 14. A copolymer preparedby the process as claimed in claim 13, wherein the diallyl ammoniummonomer to acrylamide monomer ratio is from about 5 to about 95 molepercent.
 15. A copolymer prepared by the process as claimed in claim 13,wherein the diallyl ammonium monomer to acrylamide monomer ratio is fromabout 25 to about 50 mole percent.
 16. A copolymer prepared according tothe process as claimed in claim 10 wherein the polymerizationtemperature of steps a) b) and c) is about 40° C. or below.